1. Field of the Invention
The present invention relates to Integrated Services Digital Network (ISDN) addressing, and more particularly to matching to matching ISDN destination numbers with the seven digit address number provided in the ISDN set-up packet.
2. Description of the Related Art
Computers are becoming increasingly important in many aspects of life, including homes and businesses. As computers become more important, more advances in computer capabilities are developed. One area of advancement in communication capabilities. The easier, quicker, and cheaper a computer can access data, the greater the desirability. Computers can access data through numerous media, including through telephone lines.
Originally, telephone lines were established to connect customer premises equipment (CPE) (such as a home telephone) to a central switching office of the telephone company. Original telephone lines were based on analog network technology. This technology was primarily voice-oriented and generally only allowed voice traffic transmissions. The analog network technology originally sent control signals over the same communications channel as was used to transmit voice traffic. Tones at various frequencies were used by the system as control signals. This protocol is known as in-band signaling.
Digital technology followed the analog network technology. Digital transmission technology and digital switching capabilities evolved into integrated digital networks (IDN). However, the end-user was generally unaware of any developments as these developments focused on the internal segments of the networks.
Digital development continued with the creation of out-band signaling. Out-band signaling, also referred to as common channel signaling (CCS), implements a scheme for sending control signals over a separate channel. Two types of out-band signaling schemes are available--the physical out-of-band signaling and the physical in-band/logical out-of-band signaling. An example of the latter is the Integrated Services Digital Network (ISDN). Using the ISDN scheme, both control signals and user traffic occupy the same channel. The control signals, however, are allowed only a portion of the channel while the user traffic is allotted the remaining portion.
A driving force in the advancement from analog telephony lines is the desire to access data other that voice traffic. As computer technology has progressed, the communications infrastructure has advanced to compliment newer technology. Modem communication needs of data transmission, facsimile, and video tax the capabilities of the existing analog network. However, the costs of creating a new communications infrastructure are staggering, and few if any entities are prepared to make the initial capital investment necessary to implement such a plan. This conundrum contributed to framing the goals of redesigning the telephone system, both nationally and internationally. This lead to a redesigned advanced digital system, versus the older analog systems, and is entitled the Integrated Services Digital Network (ISDN).
ISDN is designed to provide a uniform digital user network interface (UNI) and to provide a detailed standard for global usage. The ISDN scheme addresses the interface as seen by the end-user. That is the ISDN interface attaches to telephones, computer systems, and Private Branch Exchanges (PBXs). The ISDN scheme does not address how the telephone companies transmit or route the data, but only addresses the format of the data as it leaves the control of the telephone companies. The equipment and protocols implemented by the telephone companies are referred to as the carrier network. ISDN connects to the carrier network through twisted-pair, four wire digital links. ISDN implements time division multiplexing (TDM) to allow for both control signals and voice traffic to occur over the same channel. Several channel types exists:
A--4kHz analog channel; PA1 B--64 kbps digital Pulse Code Modulation (PCM) channel for data or voice traffic; PA1 C--8/16 kbps digital channel; PA1 D--16/64 kbps digital channel for out-of-band signaling; PA1 E--64 kbps digital channel for internal ISDN signaling; and PA1 F--384/1536/1920 kbps digital channel.
A typical ISDN configuration is the Basic Rate Interface (BRI), which consists of two B channels and one D channel. The BRI is usually designated as "2B+D" and is considered a standard to replace the plain old telephone system (POTS). The BRI standard is typically implemented when the ISDN is for home use or for small business operations. The BRI standard allows for the control signals to be transmitted via the D channel at the slower rate, allowing the voice traffic or data transmission to be transmitted via the B channels at the faster, 64 kbps rate. The D channel is sporadically used to transmit control signals, so during periods on non-use, the D channel can be used to transmit voice traffic or data.
When a connection is to be made between the carrier network and an ISDN device, a series of control signals are transmitted to the ISDN device. Each control signal is divided into packets, where each packet defines a parameter of the connection and the attributes of the connection. One packet, "Setup" contains the information necessary to begin the call procedure, including the callee's ISDN telephone number. The callee's ISDN telephone number is provided in the packet as a seven digit number, where this number equates to the telephone number without the area code. The ISDN device matching the number contained in the Setup packet responds with a return signal of Setup Acknowledged. To determine if the answering ISDN device is the intended ISDN device, the answering ISDN device compares the callee's ISDN address number to the ISDN device number resident in the computer system.
This number resident in the computer system is generally entered upon installation of the ISDN device. Currently in the United States, users generally enter the telephone number issued by the local telephone company for their ISDN line as the ISDN device number. Frequently the telephone number entered corresponds to the North American Numbering Plan (NANP). This plan comprises ten digits; the first three digits are commonly referred to as the area code, the next three digits are referred to as the exchange code and are used primarily in switching operations, and the last four digits identify the user line. The ISDN address number, generated by the caller's ISDN device may not contain the entire ten digit telephone number if the call is placed within a given area code. Therefore, when the callee's ISDN device compares the ISDN device address with the resident ISDN device number; the numbers may not match because of the area code. Currently, users are instructed to re-enter the ISDN device number, without the area code, to correct the matching errors. However, as the area codes become increasing important in large metropolitan areas, the necessity of entering the area code increases. Therefore, any advance in the ability of an ISDN device to contact another ISDN device, over multiple area codes, is desirable.